As is known in the art, this kind of inspection apparatus typically includes a probe chamber for performing low-temperature inspection of an inspection object (e.g., a semiconductor wafer) and a loader chamber arranged adjacent to the probe chamber. The probe chamber includes a wafer chuck for holding a semiconductor wafer and controlling the temperature thereof; a probe card arranged above the wafer chuck; and an alignment mechanism for performing alignment of a plurality of probes of the probe card and a plurality of electrode pads of the semiconductor wafer. After aligning the semiconductor wafer, the probe chamber performs specified low-temperature inspection by bringing the semiconductor wafer, which is held on the wafer chuck at a low temperature of minus tens of degrees centigrade, into electrical contact with the probes of the probe card.
The loader chamber includes a storage part for storing a plurality of semiconductor wafers on a cassette-by-cassette basis; and a transfer device having a transfer arm that transfers the semiconductor wafers between the cassette and the probe chamber. Using the transfer arm, the semiconductor wafers are taken out from the cassette one by one, pre-aligned and then transferred to the probe chamber. Upon completion of the inspection, the semiconductor wafers are transferred from the probe chamber to an original position within the cassette.
In a conventional inspection apparatus for conducting low-temperature inspection within a probe chamber (see, for example, Patent Document 1), a dry air suitable for low-temperature inspection that has a low dew point to prevent dew condensation or ice formation on a semiconductor wafer is supplied into the probe chamber, keeping the inspection environment within the probe chamber in a low-dew-point environment. Once the low-temperature inspection is completed within the probe chamber, the semiconductor wafer thus inspected is transferred from a wafer chuck in the probe chamber to a loader chamber, and then is returned to a cassette by means of a transfer arm.
With the inspection apparatus disclosed in Patent Document 1, the semiconductor wafer for which inspection has been completed undergoes dew condensation or ice formation thereon while being transferred to the cassette. This is because the semiconductor wafer is transferred from the probe chamber kept in the low-dew-point environment to the cassette within the loader chamber in which the low-dew-point environment is unavailable. It is typical that the interior of the loader chamber and the cassette is maintained in an environment similar to that of a clean room, e.g., in an environment that exhibits a temperature of 25° C. and a humidity of 50% (a dew point of 13° C.).
As an effort to prevent dew condensation or ice formation on the semiconductor wafer within the cassette, the semiconductor wafer is lifted off from the wafer chuck in the probe chamber by elevating pins, and is made to wait there for a specified time. Then, the semiconductor wafer supported on the wafer chuck is transferred back to the cassette within the loader chamber by means of the transfer arm after the temperature of the semiconductor wafer reaches the dew point of the atmosphere in the loader chamber, so that dew is prevented from being formed on the semiconductor returned to the loader chamber. However, this requires a long period of waiting time for the semiconductor wafer to reach the dew point.
To avoid the above problems, there is proposed a technique in which a space kept in a low-dew-point environment is provided in a wafer transfer device to save the above-mentioned waiting time of the semiconductor wafer in the wafer chuck. The semiconductor wafer whose inspection is completed is immediately put into the low-dew-point environment of the wafer transfer device. Then, the temperature of the semiconductor wafer is returned to a temperature at which dew condensation does not occur on the semiconductor wafer within the cassette.
(Patent Document 1) Japanese Patent No. 3,388,271
However, even if the low-dew-point environment is provided in the wafer transfer device, the environment within the cassette is still similar to that of a clean room. Therefore, to transfer the semiconductor wafer inspected at a low temperature back to the cassette, the semiconductor wafer has to wait for a specified time in the low-dew-point environment of the wafer transfer device until the temperature thereof is restored to the dew point in the cassette.
It is a recent tendency to shorten the time required for low-temperature inspection. Therefore, if the semiconductor wafer is made to wait in the low-dew-point environment of the wafer transfer device until the temperature thereof is restored to the in-cassette dew point, it is sometimes the case that a time delay occurs in supplying the next semiconductor wafer. Another problem resides in that the waiting time in the low-dew-point environment needs to be set for every inspection on a case-by-case basis according to the length of the low-temperature inspection time.